[Peter Guenther]

Back up sssist

The door locks(lock and unlock, backup assist, and some other functions are controlled by a vacum pump under the rear seat. The pump could be bad, but the good news might be a article in this months "STAR" magazine. It seems there is a hose in the pump itself that goes bad causing the pump to not do its thing. The bulletin suggests opening and replacing the hose Part# Q4 80 0001, it might be the fix, if not the pump is a pricier option. Take up the rear seat it is in foam rubber holder on passenger side, and operate the system to see if you can hear it run. You can go from there!

 

[Peter Guenther]

S Class locking

One more time.
There are two pumps, one to lock and unlock the doors the pump is under the rear seat, it does more than that, lumbar, trunk handle,some headrests and park assists. The other near the fueltank over the rear wheels closes the doors and trunk lid. There have been some bulletins namely in the last "STAR" WHERE THEY ADMIT A PROBLEM WITH THE CLOSING PART. The other is still a issue for $500-600 and no fix other than purchasing a new assembly, almost all 140 s have the issue. There are lawsuits over oil changes, why not these pums and AC issues

 

[Peter Guenther]

Pulling the (2) fuses and waiting ten seconds or so, sometimes helps if only one or two de...

Pulling the (2) fuses and waiting ten seconds or so, sometimes helps if only one or two devices dont pull in. It usually lasts for a short time, the ultimate replacement is just that!

 

[Peter Guenther]

Fuses

The fuse box in the trunk, as I recall they were in the center,look at the fuse chart

 

[Peter Guenther]

back up

Did you ever get your back up/trunk handle to function

 

[Peter Guenther]

Locking pump

I had the closing assist in the trunk go twice, I screamed and they replaced it under "cusomer satisfaction" The fuses in the trunk usually have to do with the "closing assist" doors and trunk. The pump under the seat is for locking, the back up assist, headrests in some, vacum assist for the heat/ac, and i think the seat bolsters. I dont know where the fuse is (knock on wood)and hope I dont have to search for it. The pump uns untill it sees vacum or pressue build up, which would indicate all the diaphrams are pulled in or out. If it does not see this condition in some (10sec or so)it shuts off assuming there is a leak. This where the issue of a defective hose comes from and a bulletin from MB to open the pump and replace. I guess if the motor does not run there is another issue. It is in a foam rubber container and pretty quiet lift up your rear seat and investigate

 

[Peter Guenther]

140

Here goes, you confirmed that all your devices are working, but did you ever get any noise or activity from the vacum pump? The pump supplies either vacum or pressure depending on which way the motor turns. While you have it out, and connected operate the headrests or lumbar, listen for it to whine. There was a bulletin from MB and it addressed defective (red hoses) which can be had from your dealer. but if there is no attempt to start there is a "relay" issue which causes the motor not to run. If it does run and shuts down there is a timing circuit, if it can not build up pressure or vacum. I dont recall but pricing is in the $300-400 and dont know of any other sources, purchasing from a dismantler could get you into another set of problems. There was a post from someone who went that route and got one that was not identical, there were two versions for my 92, and i would think the same applies to your year.

 

[Peter Guenther]

tipstas37 - 4/25/2004 10:59 PM

Wow......I'm about a year or so late w/this same problem. Your info is very appreciated and valuable. Pics would be great if you still have them or tell me where I can find them. I need to isolate if I need a new pump or hopefully just the hose inside that I have read postings about. My locks, rear anteneas,rear trunk lift handle, and lumbar are all inoperable. Both sets of headrests ARE working.(I heard they were related to that same pump). Also my drivers front door stop working w/the key inserted. It turns but has no resist or pressure when turning.I have to unlock the passenger door first[xx(] Do you think that is a related problem to the pump failure or just another costly coincidence? Thanks again for your previos posts!!!

All of those are controlled by the same pump, and by fuse. The rear headrests are electric in the 500SEL.